Borehole drilling



United States Patent Office 3,307,644 Patented Mar. 7, 1967 3,307,644 BOREHOLE DRILLING Henry Rowland Hill, The Warren House, Prees Heath,

Whitchurch, England Filed Dec. 6., 1963,'Ser. No. 328,587 Claims priority, application Great Britain, Dec. 6, 1962, 46,034/62 7 Claims. (Cl. 175-245) This invention relates to borehole drilling and more particularly but not essentially relates to drilling water supply boreholes.

There are two methods of drilling water supply boreholes for general use by rotary means.

One of these methods involves the use of a drill bit of which the lower cutting faces, which may be fixed rigid with the drill bit or in the form of rollers, cut on the entire cross-sectional area of the borehole so that the whole of the matter to be removed to form the borehole must be broken down into debris consisting of small particles. The drill bit is carried on the lower end of a drill pipe which is rotated to rotate the drill bit and the borehole is maintained .almost full of water and the debris is removed by introducing air bubbles into the drill pipe at the req-uired depth whereby air bubbles rise in the bore of the drill pipe and cause an upward current of Water and debris to Cccur in said bore so that the debris can be discharged at the top -of the drill pipe. Such an upward current is referred to as reverse circulation drilling by air lift. This method suffers the serious dis` advantages that (a) The cost of the drill bits is very high, particularly when the drill bits are 18 inches or more in diameter,

(b) It is not easy to determine accurately the kind of matter through which drilling is being effected and which is necessary to decide whether the matter is Water yielding,

(c) The advance of the drill bit occurs only slowly, and,

(d) It is difficult to maintain verticality of the borehole or acceptable near verticality.

It has also been proposed to employ reverse circulation drilling for mineral prospecting by drilling a borehole with a drill bit which is of relatively small diameter such as, for example approximately 4 inches, for reasons of economy and quick drilling, and the drill bit is formed with a relatively small diameter bore approximately one quarter of the external effective diameter of the drill bit which cuts on its entire lower end surface so that in addition to powdered debris being formed., a small diameter core is also formed which, however, is so small as to become broken from time to time into pieces sufficiently small as to be elevated by an upward flow of water in the drill stem or pipe and the core is removed entirely by the lift afforded by the water circulation.

The other method does not suffer the disadvantages (a), (b) and (c) above and kinvolves the use yof a hollow cylindrical drill bit of which the lower annular end in conjunction with chilled steel shot performs a cutting operation to be effected in a trepanning manner on an annular surface only of the matter being drilled so that a core is formed which enters the bore of the drill bit and said core in convenient lengths is subsequently gripped by inserted gravel wedged between the cylindrical surface of the core and an inclined annular face or faces in the bore of the drill bit and the base of the core is broken from the matter not yet drilled .and said core is then lifted out of the borehole by lifting the drill bit by the drill pipe. By the use of this method the cost of the drill bit is maintained low, the kind of matter being drilled can be accurately ascertained byl examination of -the removed cores, the rate of advance of the drill bit is relatively fast and the borehole can be maintained more nearly vertical than with the other method since the cylindrical drill bit is guided over the length of the drill bit by the borehole just drilled. This method of borehole drilling may be referred to as core borehole drilling and it is with this method of core borehole drilling that the present invention is concerned.

Core borehole drilling is performed at present with what may be referred to as forward or normalcirculation drilling and lthis involves passing water down the drill pipe to the lower cutting end of the drill bit and the debris and water is carried away from the lower end of the drill bit around the external cylindrical surface of the drill bit and thus between the external cylindrical surface of the drill bit and the wall of the borehole and the debris rises in the borehole externally of the drill pipe and on reaching the top of .a bucket a-t the top of the drill bit the heavier debris falls into the bucket and when the drill pipe, bucket and drill bit are lifted to remove a core from the borehole the debris in the bucket and the core are examined lto try to ascertain the nature of the matter being drilled. Suspended matter accumulates in the borehole and can prove to be most troublesome during drilling and, when recommencing drilling after temporary cessation, unless removed.

This known Way of performing core borehole drilling suffers the following disadvantages (e) Water containing debris is forced outwardly from the borehole into the crevices or fissures between strata, and this may be assisted by any extraction by pumping from other boreholes in the vicinity, so that when a sample of Water yielded by the borehole is required to be taken for test purposes all dirty water containing debris must first be drained from the bore-hole to clean the crevices and this can take a matter of days.

(f) It is not easy to obtain absolute or acceptable near verticality of the hole due to the abrasive action of debris between the external cylindrical surface of the drill bit and the wall of the borehole and this is more serious when drilling in soft and medium hard matter such as sandstone.

(g) Due to the debris between the external cylindrical surface of the drill bit and the wall of the borehole the drill bit sometimes becomes fast in the bore -usually when water circulation fails, and cannot be removed or can only be removed with great diiculty and after protracted efforts.

(h) The chilled steel shot inserted for cutting purposes is not all `used to the best advantage and metal dust formed by the drilling operation can permanently choke fissures in the borehole.

(i) The gravel inserted for removing the core is not always used to the best advantage.

(j) the outward pressure of the dirty water in the borehole being drilled can cause adjacent boreholes in use to yield dirty water.

It is an object of the present invention to provide a core drill bit for core borehole drilling which avoids or lessens the disadvantages (a) to (j) above.

According to this aspect of the present invention there is provided a core drill bit for core borehole drilling comprising a lowerrnost drill pipe having attachment means at its upper end for attachment to the lower end of an upper drill pipe, a hollow cylindrical drill bit having a cylindrical wall of substantially larger diameter than said lowerrnost drill pipe and `secured to the lower end of the lowerrnost drill pipe and provided at its lower end with a cutting part and the bore wall of the hollow cylindrical drill bit adjacent the lower end thereof having an upwardly divergent face to Wedge recovery material against a core, a hollow directing member disposed in the bore of the hollow cylindrical drill bit and including a slidarelatively axially slidable and rotatable and said member having a passage extending from the lower end of the l'enlargement adjacent the periphery thereof Where said 'passage communicates with the interior of the hollow cylindrical drill bit at a position closely adjacent the bore of the cylindrical wall thereof and extending to the upper end of the slidable pipe to communicate with the bore of the lowermost drill pipe and said passage having a cross-sectional area substantially less than that of the bore of the hollow cylindrical drill bit so as to enable the speed of ow of liquid and debris upwardly through an annular clearance space between -a substantially cylindrical surface of the core and the bore of the hollow cylindrical drill bit to be maintained in the passage and in the bore of the lowermost drill pipe.

It should be appreciated that the invention enables the debris to be washed away from the lower cutting end of the cylindrical drill bit by water or other liquid entering the borehole from the matter, if yielding, being drilled and that as the rate of flow of the debris and water or other liquid is at least maintained or substantially maintained between said lower cutting end and the bore of the drill pipe the debris is not allowed to settle and remain `at t-he bottom of the borehole. As the water or other liquid is being delivered into the bore from the matter being drilled the crevices or fissures and various stratay in the matter remain clean and thus` enable a sample of the Water or other liquid delivered by the borehole to be obtained quickly after cessation of drilling for testing. Furthermore as debris is not disposed Ibetween the exterior of the cylindrical drill bit and the wall of the borehole the drill bit is not liable to become wedged fast in the borehole and the borehole is maintained vertical or substantially so.

It should be further appreciated that yield water or other liquid will enter the borehole and will tend to settle at its normal level or table usually below the top of the borehole and it is desirable during drilling that the water or other liquid level shall be kept at a level below this normal level which will ensure that yield water or other liquid is flowing into the borehole and in order to balance the discharge water or other liquid containing the debris with the Water or other liquid entering the borehole it may be necessary continually to charge the borehole through the top thereof by clean water or other liquid from an external supply pipe, or by discharged water or other liquid after it has passed through settling chambers to remove the debris.

Further objects and advantages will be obvious from the following description.

The invention -will now be more particularly described with reference to the accompanying drawings in which:

FIGURE 1 is a sectional view of a hollow cylindrical drill bit shown in position in a borehole being drilled for Water,

FIGURE 2 is an enlarged fragmentary view of FIG- URE 1,

FIGURE 3 is a cross-sectional view of FIGURE 1 on the lines` 3 3 thereof, and,

FIGURE 4 is a fragmentary cross-sectional view similar to FIGURE 2 b-ut showing a modification.

Referring to FIGURES l to 3 the matter being drilled is indicated at 1t) and it should be appreciated that this includes all varying kinds of strata normally encountered when drilling boreholes.

Drill pipes 11 are employed which are rotated by known means and are connected together in end-to-end relation as required and conveniently each drill pipe is formed at an upper end with an attachment means formed by a screw-threaded tapering socket 12 and at its lower end with a screvv-threaded tapering spigot 13 and the spigot 13 of an upper drill pipe engages in a fluid-tight manner with the screw-threaded socket at the upper end of a lower drill pipe.

Secured to the lowermost drill pipe 22 is a hollow cylindrical drill bit indicated at 14 of substantially larger diameter than said lowermost drill pipe for example at least four times larger, and said bit comprises an upper cylindrical part 15 and a lower cylindrical cutting part 16 and the two parts 15 and 16 are removably connected together by screw means 17. The external diameters of the parts 15 and 16 are equal and correspond approximately to the required diameter of the borehole and the lower edge 18 of the cutting part is formed with gaps 19 to receive the normally used chilled steel shot 46 for cutting purposes.

The lower cylindrical part 1,6 is thicker than the upper part 15 as clearly shown in the drawings and at the upper end of said lower part 16 the bore is provided with an inclined annular face 20 which diverges upwardly as shown in the drawings.

Disposed approximately mid-way of the height of the cylindrical drill bit 14 and within the bore thereof is an annular platform 21 and secured to this platform 21 is the lowermost drill pipe 22 provided at its upper end with a socket 12 and at the upper end of the cylindrical drill bit the drill pipe 22 is supported centrally in the bore of the drill bit lby a plurality of radial webs 23 which, however, are arranged so that the upper end of the drill bit 1s open.

The upper part of the cylindrical drill bit defined by the cylindrical upper part 1S and the platform 21 constitutes a bucket which is open at its upper end and formed in the wall of the upper part 15 are a plurality of holes 24- which are level with the upper surface of the platform 21 and through which chilled steel shot 46 can pass from the interior of the bucket to the exterior of the drill bit. Disposed -above the holes 24 is a larger hole 25 which forms an inspection window and it should be appreciated that, during drilling, the mixture of water and debris in the vicinity of and above the drill bit is in a state of agitation whereas when drilling is stopped the agitation also stops or is substantially decreased and debris above the bucket will fall and settle in the bucket and can then be inspected through said window 2S when the drill bit is removed from the borehole.

Disposed in main within the lower part of the cylindrical drill bit is a hollow directing member 26 which comprises a semi-buoyant, i.e. an almost buoyant charnber 27 secured to the lower end of a slidable pipe 28 approximating in cross-sectional area to that of the lowermost drill pipe 22.

The upper end of the slidable pipe 2S is provided with a guide sleeve 29 which slidably engages with a small clearance, for example, 1/16-inch in diameter, the bore of the lowermost drill pipe 22 so that the directing member 26 is capable of sliding vertically relative to the lowermost drill pipe.

The almost buoyant chamber 2'7 forms an enlargement at the lower end of the slidable pipe and is of cylindrical formation and includes upper and lower horizontal end plates 311 and 31 respectively to which is secured a cylindrical side wall 32 the external diameter of which is slightly less than the bore diameter of the upper part 15 of the drill bit and the cylindrical wall 32 has secured thereto adjacent its upper end and adjacent its lower end four bearing pads 33 which are equi-angularly spaced apart and bear, with a slide fit, against the bore Wall of the upper part 15 so as to support the almost buoyant chamber 27 transversely co-axially within the cylindrical drill bit.

In order that the chamber should be capable of withstanding the water pressures to which it is subjected at great depths said chamber is provided with radial webs 42 which extend between the slidable pipe 28 and the cylindrical wall 32.

There is thus provided an annular clearance space between the bore wall of the drill bit and the almost buoyant chamber and it is desirable that the radial width of this space should be as small as is reasonably possible and it is possible to achieve this by making the lower cutting part 16 of the drill bit removable from the upper part 1S as previously described to permit of the insertion of the chamber into the upper part 15.

The hollow directing member 26 provides a passage of which an upper part is formed by the slidable pipe 28 which extends downwardly into the almost buoyant chamber 27 and said upper part communicates with a lower upwardly convergent passage part 34 which opens at its lower end in the vicinity of the junction of the lower end plate 31 and the cylindrical side wall 27 and may open at its lower end onto the cylindrical wall 32 or onto the lower horizontal end plate 31 or partly onto both. The lower passage part 34 is formed between an upper truste-conical piate 35 secured to the lower end of the slidable pipe 28 and a lower conical plate 48 secured to the lower horizontal end plate 31 and said plates 35 and 48 are supported by radial webs 36 and form an upwardly convergent structure.

It should be appreciated that the bore of the slidable pipe 28 communicates at its lower end with the upper end of the passage 34 which communicates at its lower end with the bore ofthe cylindrical drill bit at a position closely adjacent the bore wall of said drill bit.

In the modification shown in FIGURE 4 the semibuoyant chamber 50 instead of being formed with a single lower passage part 34, is formed with four lower passage parts 49 which are formed by an upwardly convergent structure and each part is upwardly convergent at its lower end in the vicinity of the junction of the lower end plate 51 and the cylindrical side wall 52 and these passage parts are equi-angularly spaced apart.

The inclined passage part or parts in both forms, forms or form a conical structure which serves to reinforce the lower end of the hollow directing member.

The method of drilling the borehole and removing a core and testing the yield water proceeds as follows.

The upper end of the borehole is initially formed in earth in any known manner and when hard matter is encountered the cylindrical drill bit 14 is inserted in the borehole and is rotated in the normal manner by the drill pipes 11. At this stage it may be necessary to charge the borehole with water if the borehole is not yielding but eventually when the borehole begins to yield the yield water tends to attain its natural water level or table and during drilling the water level in the borehole is maintained at approximately 3 feet below its natural level. If the yield water is not sucient to balance the discharge water containing debris then it is necessary to add additional water to the borehole through the top thereof from an external supply of clean water or discharged water after kit has passed through settling chambers to remove the debris, but this additional water is not passed into the borehole if sufficient yield water is being provided to balance the discharge water. By maintaining the level of the water in the borehole at a distance below the natural water level the borehole is caused to deliver yield water if possible.

Any air which might be trapped in the lower end of the drill bit when said drill bit is immersed in the water in the borehole can escape upwardly into the drill pipes by passing between the guide sleeve 29 and the slidable pipe 28.

In order that the lower end of the cylindrical drill bit 15 shall create a cutting action on the matter in which the borehole is being drilled chilled steel shot 46 is dropped into the borehole in a continuous trickle feed or in measured quantities and drops onto the platform 21 in the bucket at the upper end of the drill bit and passes outwardly through the holes 24 and down between the external cylindrical surface of the drill bit and the wall of the borehole 37 and downward movement of the steel shot is assisted by the downward flow of the yield water from the borehole as hereinafter described. The steel shot falls to the bottom of the borehole and in conjunction with the lower edge 18 of the drill bit causes a cutting action to be exercised on the matter 10 being drilled. If the matter being drilled is of a very hard nature so that cutting clearances formed externally of the drill bit are small then the shot 46 is fed through an air supply tube 53 hereinafter referred to and water pressure applied downwardly through the drill pipe 11 is used to eject the shot downwardly through the passage part 34 (or passage parts 49) to the bottom of the borehole and the lower edge 18 of the drill bit.

The cylindrical drill bit 14 drills an annular hole and thus forms a cylindrical core 38 and the cutting action is such that a clearance 39 is provided between the exterior of the drill bit 14 and the wall of the bore 37 and a clearance 40 is provided between the interior of the drill bit and the external cylindrical surface of the-core 38.

As drilling proceeds the core 38 rises within the bore of the drill bit 15 and the lower end plate 31 of the almost buoyant chamber 27 (or the lower end plate `51 of the chamber 50) rests on the upper end face 41 of the core and as drilling proceeds the drill pipe 22 moves downwardly or telescopes over the slidable pipe 28 which remains vertically stationary.

It should be appreciated that as the chamber 27 (or 50) is almost buoyant which is achieved by weights it rests on the top of the core 38 without, however, a severe abrasive action being created so that the lower end plate 31 (or 51) is not quickly worn away.

During the drilling action yield water with or without a supply of water through the top of the borehole, enters the borehole and the water is maintained in the borehole at an operating level below the normal water rest level or table and this water therefore partially ills the borehole and fills the passage part 34 (or passage parts 49) and drill pipes 11, 22 and slidable pipe 28 and a reverse circulation flow is created by the air supply tube 43 in the drill pipes and which tube 43 is provided at its lower end with a removable discharge head 44 formed around its upper end with a plurality of smal-l openings or nozzles 45 and open at its lower end and through which openings Vor nozzles compressed air is pumped so as to enter the drill'pipes and rise so as to cause an upward ow of water in the drill pipes. Thus an upward flow of water occurs also in the passage 34 and in the space 40 between the core 38 and the bore of the drill bit 15 whilst a downward ow of water occurs in the space 39 between the drill bit and the wall of the bore 37 and this water is yield water supplied through crevices and the like in the wall of the bore and which crevices are thus maintained in a flushed clean condition. It follows therefore that debris created by the drilling operation at the lower end of the drill bit passes from the lower end edge 18 of the drill bit up the space 40 which, being of a clearance nature only, causes the water and debris therewith to move upwardly at a substantial speed and as the lower end of the passage part 34 (or passage parts 49) is or are disposed closely adjacent the bore of the cylindrical drill bit the water and debris passes immediately into said passage without loss of speed and thus without the debris losing its inertia. The total cross-sectional area provided by the passage part 34 (or passage parts 49) is arranged as near as possible so as to approximate to the cross-sectional area of the space 40 so that the speed of ilow of water and debris through the space 4i) is at least maintained or substantially maintained between the space 40 and the passage in the hollow directing member, and

also in the said passage 34 and in this way the debris is removed from the borehole without losing its inertia and thus without being able to settle in any substantial quantities.

If the core being formed by the drilling operation should crack or collapse, the debris formed thereby will also be removed through the drill pipe.

Due to the lowermost drill pipe 22 having a larger bore diameter than the slidable pipe 28, the speed of flow of the water and debris would appear to tend to decrease and thus the debris would tend to lose its inertia but the speed of flow and thus the inertia of the debris is maintained by a restricted flow of clean water which is drawn upwardly into the lower drill pipe 22 through the small clearance between said pipe and the guide sleeve 29.

During the upward ow of water and debris in the drill pipe 22 the clean water which passes upwardly between said pipe and the guide sleeve 29 will also ensure that no debris will foul the clearance between said pipe and guide sleeve during drilling.

If it is required to test a sample of the yield water of the borehole it is only necessary to stop drilling and a short time after clean yield water can be pumped out of the drill tube by use of compressed air passed down the tube 43.

In order to extract a core 38 drilling is stopped and the tube 43 is removed from the drill pipe and then an estimated quantity of known spherical recovery gravel (not shown) or like wedge operated gripping means is inserted into the drill pipe and this falls through the directing member 26 onto the lower conic-al plate 48 whereby all the introduced gravel passes down the passage 34 and becomes wedged between the inclined annular face of the drill bit and the cylindrical surface of the core 38 and by applying a lifting force to the drill pipes the drill pipe 22, being secured to the cylindrical drill bit 14, raises said drill bit and the gravel is caused, by the inclined annular face 20 to grip the core which is then lifted out of the borehole.

It should be appreciated that the bearing pads 33 can rest on the inclined annular face 20 to prevent the chamber 27 falling downwardly out of the lower end of the drill bit 15.

'Instead of using chilled steel shot for effecting the cutting action, the lower end of the cylindrical drill bit may be provided with known kinds of rOller cutting bits.

The following advantages are obtained by the invention.

The borehole and the matter providing the wall of the borehole is maintained clean at all times owing to yield water from the borehole being constantly delivered into the borehole for drilling purposes, changes of the matter being drilled can immediately be noted at the surface where the debris is being discharged and the removed cores, the drill bit cannot become locked fast in the borehole because debris, recovery gravel and shot dust etc. does not accumulate between the exterior of the cylindrical drill and the borehole and this also results in the borehole being drilled vertically or near vertically, samples of yield water can be taken at any time without time being lost for allowing the borehole to become clean, owing to the absence of debris at the termination of drilling, pumping by mechanical pumps can be immediately 4started and there is no danger of the mechanical pumps being damaged, the supply of all the chilled steel shot to the lower end of the drill bit is assured and the supply of all the recovery gravel to the inclined annular face 20 is assured and the yield from boreholes adjacent the borehole being drilled is not adversely affected.

It is emphasized that the invention is only concerned with core borehole drilling in which relatively large diameter cores of between approximately 11/2 feet and 8 feet in diameter are formed and must be lifted out of the borehole by lifting the drill bit because cores of these sizes cannot be lifted merely by a lifting effort afforded by a water current such as might be possible with mineral drill bits of relatively small diameter. Furthermore drill bits in the order of 11/2 feet to 8 feet in diameter may be respectively approximately 30 feet to l5 feet in length and the lower half of the drill bit affords a core receiving bore which thus affords an extremely large capacity reservoir and if reverse circulation were attempted, other than in accordance with the present invention, owing to a limited speed of flow being permitted by the clearance between the drill bit and the matter being drilled, the reservoir would become an almost static reservoir as regards water circulation and the debris would sink onto the top of the core and quickly fill the bottom of the reservoir and thus would quickly completely stop water circulation and thus the drilling.

The invention thus provides an improved method and apparatus for core borehole drilling by what is known as a reverse circulation process.

What I claim then is:

1. A core drill bit for core borehole drilling comprising a lowermost drill pipe having attachment means at its upper end for attachment to the lower end of an upper drill pipe, a hollow cylindrical drill bit having a cylindrical wall of substantially larger diameter than said lowermost drill pipe and secured to the lowermost drill pipe and provided at its lower end with a cutting part and the bore Wall of the hollow cylindrical drill bit adjacent the lower end thereof having an upwardly divergent face to wedge recovery material against a core, a hollow directing member disposed in the bore of the hollow cylindrical drill bit and including a slidable pipe the cross-sectional area of which approximates to that of the lowermost drill pipe and the upper end of said slidable pipe having a sliding and rotatable engagement with the lower end of the lowermost drill pipe and also including at the lower end of the slidable pipe an enlargement of which the lower end can rest on an upper end face of the core and the external diameter of the enlargement being slightly less than the bore diameter of said drill bit to enable the member and the drill bit to be relatively axially slidable and rotatable and said member having a passage extending from the lower end of the enlargement adjacent the periphery thereof where said passage communicates with the interior of the hollow cylindrical drill bit at a position closely adjacent the bore of the cylindrical wall thereof and extending to the upper end of the. slidable pipe to communicate with the bore of the lowermost drill pipe and said passage having a cross-sectional area substantially less than that of the bore of the hollow cylindrical drill bit so as to enable the speed of flow of liquid and debris upwardly through an annular clearance space between a substantially cylindrical surface of the core and the bore of the hollow cylindrical drill bit to be maintained in the passage and in the bore of the lowermost drill pipe.

2. A core drill bit according to claim 1 comprising a conical structure at the lower end of the enlargement of the hollow directing member and in which conical structure a lower part of the passage is formed and said lower part is inclined upwardly from the periphery of the enlargement at the lower end of which a plate is provided to rest on the upper end face of the core.

3. A core drill bit according to claim 1 wherein the enlargement at the lower end of the hollow directing member is formed by an almost buoyant fluid-tight chamber.

4. A core drill bit according to claim 1 wherein the hollow cylindrical drill bit at the upper end of the cylindrical wall thereof is open and the lower end of the lowermost drill pipe is secured to a platform disposed in the drill bit below the upper open end thereof and above the enlargement of the hollow directing member andthe cylindrical wall above the platform provides a bucket formation.

5. A core drill bit according to claim 4 wherein a window opening is formed in the cylindrical wall of the bucket formation through which the nature of the debris in the bucket formation can be examined.

6. A -core drill bit according to claim 4 wherein a hole is formed in the cylindrical wall of the bucket formation level with the platform and through which hole chilled steel shot can pass out of the Ibucket formation to the exterior of the drill bit.

7. A core drill bit for core borehole drilling comprising a lowermost drill pipe having attachment means at its upper end for attachment Vto the end of an upper drill pipe, a hollow cylindrical drill -bit having a cylindrical wall of substantially larger diameter than said lowermost drill pipe and within which cylindrical wall said lowermost drill pipe is disposed co-axially therewith and said lowermost drill pipe being secured at its lower end to -a hori- Zontal platform disposed across the bore of the drill bit and secured thereto intermediate the upper and lower ends thereof whereby the drill bit can be rotated by the lowermost drill pipe and the upper end of the cylindrical wall defining an opening whereby a bucket formation is provided by said cylindrical wall and platform, said cylindrical wall being provided at its lower end with a cutting part and the bore wall of the hollow cylindrical drill bit adjacent the lower end thereof having an upwardly divergent face to wedge recovery material against a core, web means lbetween the upper end of the cylindrical wall and the upper lowermost drill pipe to support the lowermost drill pipe, a window opening in the cylindrical wall of the drill bit adjacent the lower end of the bucket formation, Aa hole in the cylindrical Wall level with the platform, a hollow directing member disposed in the bore of the hollow cylindrical drill bit and including a slidable pipe disposed co-axially within the cylindrical wall of the drill bit and having telescopic engagement at its upper end with the bore of the lowermost drill pipe and there being a small clearance between said upper end and the bore of the lowermost drill pipe, and said member also including an enlargement at the lower end of the slidable pipe and said enlargement affording a closed almost buoyant chamber of which the external diameter is only slightly smaller than the bore diameter of the cylindrical bore and said chamber having bearing means bearing against the cylindrical bore to prevent transverse movement of said chamber relative to the cylindrical wall whilst permitting relative rotational and axial movement of the cylindrical wall and charnber, a conical structure at the lower end of the enlargement, said hollow directing member having a passage extending from the upper end of the slidable pipe where it communicates with the bore of the lowermost drill pipe to the lower end of the conical structure where said passage communicates with the interior of the hollow cylindrical drill bit at a junction of said lower end and a cylindrical wall of the chamber and adjacent the bore of the cylindrical Wall of the drill bit and said passage having a cross-sectional area substantially less than that of the bore of the hollow cylindrical drill bit, and a base plate on the chamber to rest against an upper end face on the core when formed in the bore of the drill bit.

References Cited by the Examiner UNITED STATES PATENTS 1,071,199 8/1913 Andrews 175--60 X 2,537,605 1/1951 Sewell 175-60 X 2,727,727 12/1955 Williams 175-54 2,789,790 4/1957 Kirby 175-245 21,927,776 3/1960 Hildebrandt 175-245 X 3,086,602 4/1963 Henderson 175-60 X CHARLES E. OCONNELL, Primary Examiner.

N. C. BYERS, Assistant Examiner. 

7. A CORE DRILL BIT FOR CORE BOREHOLE DRILLING COMPRISING A LOWERMOST DRILL PIPE HAVING ATTACHMENT MEANS AT ITS UPPER END FOR ATTACHMENT TO THE END OF AN UPPER DRILL PIPE, A HOLLOW CYLINDRICAL DRILL BIT HAVING A CYLINDRICAL WALL OF SUBSTANTIALLY LARGER DIAMETER THAN SAID LOWERMOST DRILL PIPE AND WITHIN WHICH CYLINDRICAL WALL SAID LOWERMOST DRILL PIPE IS DISPOSED CO-AXIALLY THEREWITH AND SAID LOWERMOST DRILL PIPE BEING SECURED AT ITS LOWER END TO A HORIZONTAL PLATFORM DISPOSED ACROSS THE BORE OF THE DRILL BIT AND SECURED THERETO INTERMEDIATE THE UPPER AND LOWER ENDS THEREOF WHEREBY THE DRILL BIT CAN BE ROTATED BY THE LOWERMOST DRILL PIPE AND THE UPPER END OF THE CYLINDRICAL WALL DEFINING AN OPENING WHEREBY A BUCKET FORMATION IS PROVIDED BY SAID CYLINDRICAL WALL AND PLATFORM, SAID CYLINDRICAL WALL BEING PROVIDED AT ITS LOWER END WITH A CUTTING PART AND THE BORE WALL OF THE HOLLOW CYLINDRICAL DRILL BIT ADJACENT THE LOWER END THEREOF HAVING AN UPWARDLY DIVERGENT FACE TO WEDGE RECOVERY MATERIAL AGAINST A CORE, WEB MEANS BETWEEN THE UPPER END OF THE CYLINDRICAL WALL AND THE UPPER LOWERMOST DRILL PIPE TO SUPPORT THE LOWERMOST DRILL PIPE, A WINDOW OPENING IN THE CYLINDRICAL WALL OF THE DRILL BIT ADJACENT THE LOWER END OF THE BUCKET FORMATION, A HOLE IN THE CYLINDRICAL WALL LEVEL WITH THE PLATFORM, A HOLLOW DIRECTING MEMBER DISPOSED IN THE BORE OF THE HOLLOW CYLINDRICAL DRILL BIT AND INCLUDING A SLIDABLE PIPE DISPOSED CO-AXIALLY WITHIN THE CYLINDRICAL WALL OF THE DRILL BIT AND HAVING TELESCOPIC ENGAGEMENT AT ITS UPPER END WITH THE BORE OF THE LOWERMOST DRILL PIPE AND THERE BEING A SMALL CLEARANCE BETWEEN SAID UPPER END AND THE BORE OF THE LOWERMOST DRILL PIPE, AND SAID MEMBER ALSO INCLUDING AN ENLARGEMENT AT THE LOWER END OF THE SLIDABLE PIPE AND SAID ENLARGEMENT AFFORDING A CLOSED ALMOST BUOYANT CHAMBER OF WHICH THE EXTERNAL DIAMETER IS ONLY SLIGHTLY SMALLER THAN THE BORE DIAMETER OF THE CYLINDRICAL BORE AND SAID CHAMBER HAVING BEARING MEANS BEARING AGAINST THE CYLINDRICAL BORE TO PREVENT TRANSVERSE MOVEMENT OF SAID CHAMBER RELATIVE TO THE CYLINDRICAL WALL WHILST PERMITTING RELATIVE ROTATIONAL AND AXIAL MOVEMENT OF THE CYLINDRICAL WALL AND CHAMBER, A CONICAL STRUCTURE AT THE LOWER END OF THE ENLARGEMENT, SAID HOLLOW DIRECTING MEMBER HAVING A PASSAGE EXTENDING FROM THE UPPER END OF THE SLIDABLE PIPE WHERE IT COMMUNICATES WITH THE BORE OF THE LOWERMOST DRILL PIPE TO THE LOWER END OF THE CONICAL STRUCTURE WHERE SAID PASSAGE COMMUNICATES WITH THE INTERIOR OF THE HOLLOW CYLINDRICAL DRILL BIT AT A JUNCTION OF SAID LOWER ENE AND A CYLINDRICAL WALL OF THE CHAMBER AND ADJACENT THE BORE OF THE CYLINDRICAL WALL OF THE DRILL BIT AND SAID PASSAGE HAVING A CROSS-SECTIONAL AREA SUBSTANTIALLY LESS THAN THAT OF THE BORE OF THE HOLLOW CYLINDRICAL DRILL BIT, AND A BASE PLATE ON THE CHAMBER TO REST AGAINST AN UPPER END FACE ON THE CORE WHEN FORMED IN THE BORE OF THE DRILL BIT. 